FIG. 1 shows a coordinate system for illustrating a conventional method for controlling a braking system. The conventional method for controlling the braking system is discussed, for example, in DE 10 2008 004 201 A1.
The x-axis of the coordinate system of FIG. 1 indicates a setpoint overall braking torque Mges-soll requested by a driver of a vehicle equipped with the relevant braking system. The requested setpoint overall braking torque Mges-soll may also be described as a driver braking intention and may be ascertained, for example, via an adjustment travel of a brake actuating element (pedal travel). An actual engine braking torque Mmot-ist which is exerted by a motor or generator is represented as the y-axis of the coordinate system of FIG. 1.
As long as the setpoint overall braking torque Mges-soll lies below a minimum braking torque MO defined by a free travel of the braking system, the requested setpoint overall braking torque Mges-soll is exerted fully as the actual engine braking torque Mmot-ist on the respective wheels or axles of the vehicle with the aid of the motor or generator. Only after the free travel is ended when a setpoint overall braking torque Mges-soll equals the minimum braking torque MO does the driver brake directly via a brake actuating element connected to a brake master cylinder of the braking system into the two brake circuits also connected to the brake master cylinder. In order for a sum of the actual engine braking torque Mmot-ist and an overall (not shown) actual friction braking torque of all wheel brake cylinders of the braking system to remain the same as the setpoint overall braking torque Mges-soll, the actual engine braking torque Mmot-ist must be reduced once a setpoint overall braking torque Mges-soll is equal to the minimum braking torque MO.
If the driver brakes into both brake circuits, the actual engine braking torque Mmot-ist is reduced to zero, which is represented in graph 2. In the conventional method represented herein, however, one of the two brake circuits may also be decoupled from the brake master cylinder by a closing of a shut-off valve. Once the shut-off valve is closed, the cancelled braking effect of the wheel brake cylinders of the decoupled brake circuit may be used to set the actual engine braking torque to unequal to zero, which is represented by graph 4.